The present invention relates to a layer insulating film for multilayer interconnection of semiconductors which comprises a fluorine-containing polybenzoxazole resin, and a process for producing the resin used therefor.
Inorganic insulating films using silicon dioxide formed by the chemical vapor deposition method, etc. have been in use as a material for layer insulation. However, though the films have a high heat resistance, they have not sufficiently good performance characteristics to meet the requirements related to semiconductor uses of recent years.
On the other hand, polyimide resins have been extensively studied as an organic insulating film which exhibits an excellent flatness and low dielectric constant, but they have a problem in resistance to moisture absorption and hence cannot be considered to have satisfactory performance characteristics as a material for layer insulating film.
Similar studies have also been made of polybenzoxazole resins. One of the processes for producing polyhydroxyamide resin, the precursor of polybenzoxazole resin, is an acid chloride method which allows a dicarboxylic acid dichloride to react with a bis(aminophenol) compound; but since chloride ions formed in the course of the synthesis get mixed as an impurity, the resulting resin is not so much preferable for use as a semiconductor material. Another method which does not involve the risk of contamination by chloride ions is the DCC method which uses dicyclohexylcarbodiimide (hereinafter abbreviated as DCC) and directly obtains polyhydroxyamide resin from a dicarboxylic acid and a bis(aminophenol) compound. However, when a material of low reactivity as 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane is used in the DCC method, the polyhydroxyamide resin obtained has a low molecular weight, and does not have satisfactory heat resistance, strength, etc.
The object of the present invention is, overcoming the above-mentioned problems of the prior art, to provide a layer insulating film for multilayer interconnection of semiconductors excellent in resistance to heat, resistance to moisture absorption and additionally excellent in electric characteristics and a process for producing a resin used therefor.
The present inventors have made extensive study to solve the above-mentioned problems of previous layer insulating film material for multilayer interconnection. As a result, the inventors have found a fluorine-containing polybenzoxazole resin excellent in resistance to heat, resistance to moisture absorption and further in electric characteristics having the structure represented by the formula (6) and obtained by a production process which comprises subjecting to heat-dehydrating ring-closure (A) a fluorine-containing polyhydroxyamide resin having the structure represented by the formula (1) and obtained by reacting a dicarboxylic acid diester obtained by purifying a product obtained by the reaction of at least one kind of compound selected from the group of compounds represented by-the formulas (2) with 2,2xe2x80x2bis-(trifluoromethyl-4,4xe2x80x21-biphenyldicarboxylic acid, with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane; or (B) a fluorine-containing polyhydroxyamide resin obtained by reacting a product obtained by replacing less than 50% by mole of 2,2xe2x80x2-bis(trifluoromethyl)-4,4xe2x80x2-biphenyldicarboxylic acid diester by a dicarboxylic acid diester obtained by purifying a product obtained by the reaction of a dicarboxylic acid represented by R of the formula (3) with one kind of compound selected from the group of compounds represented by the formulas (2), with a product obtained by replacing less than 50% by mole of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane by a bisaminophenol represented by Rxe2x80x2of the formula (3). The present invention has been accomplished on the basis of the above finding. 
wherein m is an integer of 10-500, 
wherein X and Y each independently represent a structure selected from the formulas (4), 
wherein Z represents a structure selected from the formulas (5), provided that the hydrogen atom(s) on the benzene ring in these structures may be substituted with at least one member selected from the group consisting of methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, fluorine atom and trifluoromethyl group. 
wherein, in the formula (6), m is an integer of 10-500.
In the present invention, the fluorine-containing polyhydroxyamide resin having the structure represented by the formula (1) is produced by the reaction of a diamine component and a dicarboxylic acid component, the diamine component used being 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.
The dicarboxylic acid component used is a dicarboxylic acid diester obtained by the reaction of 2,2xe2x80x2-bis-(trifluoromethyl)-4,4xe2x80x2-biphenyldicarboxylic acid with one kind of compound selected from the group of compounds represented by the above-mentioned formulas (2), e.g., 1-hydroxybenzotriazole, 4-nitro-phenol, 2-mercaptobenzoxazole, and the like. Among the group of compounds represented by the formulas (2), more preferably be used is 1-hydroxybenzotriazole.
As to the diamine component, the intended effect of the present invention can be attained also when a part of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane is replaced by a bisaminophenol compound represented by Rxe2x80x2of the formula (3), provided that the replaced part must be less than 50% in terms of molar ratio of monomer. The bisaminophenol compound represented by Rxe2x80x2of the formula (3) may be, for example, 2,4-diaminoresorcinol, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 1,4-bis(3-amino-4-hydroxyphenyl)tetrafluorobenzene, 3,3xe2x80x2-diamino-4,4xe2x80x2-dihydroxybiphenyl, 3,3xe2x80x2-diamino-5,5xe2x80x2, 6,6xe2x80x2-tetrafluoro-4,4xe2x80x2-dihydroxybiphenyl, 2,2-bis(3-amino-4-hydroxy-5-trifluoromethylphenly)hexafluoropropane, 2,2-bis(4-amino-3-hydroxy-5-trifluoromethylphenyl)hexafluoropropane, 2,2-bis(3-amino-4-hydroxy-5-pentafluoroethylphenyl)hexafluoropropane, 2-(3-amino-4-hydroxy-5-trifluoromethylphenyl)-2-(3-amino-4-hydroxy-5-pentafluoroethylphenyl)hexafluoropropane, etc., but it is not limited thereto.
As to the dicarboxylic acid component, like in the case of the bisaminophenol compound, the intended effect of the present invention can be attained also when a part of 2,2xe2x80x2-bis(trifluoromethyl)-4,4xe2x80x2-biphenyldicarboxylic acid is replaced by a dicarboxylic acid represented by R of the formula (3), provided that the replaced part must be less than 50% in terms of molar ratio of monomer. The dicarboxylic acid represented by R of the formula (3) may be, for example, 5-fluoroisophthalic acid, 2-fluoroisophthalic acid, 3-fluorophthalic acid, 4-fluorophthalic acid, 2-fluoroterephtalic acid, 2,4,5,6-tetrafluoroisophthalic acid, 3,4,5,6-tetrafluorophthalic acid, 4,4xe2x80x2-hexafluoroisopropylidenediphenyl-1,1xe2x80x2-dicarboxylic acid, perfluorosuberic acid, terephthatic acid, isophthalic acid, 4,4xe2x80x2-oxydiphenyl-1,1xe2x80x2-dicarboxylic acid, etc., but it is not limited thereto.
For the synthesis of the dicarboxylic acid diester in the present invention, 2,2xe2x80x2-bis(trifluoromethyl)-4,4xe2x80x2-biphenyldicarboxylic acid and one kind of compound selected from the group of compounds represented by the above-mentioned formulas (2) are dissolved in an anhydrous organic solvent, such as 1,4-dioxane, ethyl acetate, tetrahydrofuran, dimethylformamide, N-methyl-2-pyrrolidone, etc., preferably a condensing agent such as dicyclohexylcarbodiimide, etc., is added thereto at xe2x88x9210 to 5xc2x0 C., and thereafter the resulting mixture is allowed to react preferably at 15 to 25xc2x0 C. for 18-24 hours.
The reaction mixture thus obtained is filtered, the filtrate is concentrated by means of an evaporator, a poor solvent, such as diethyl ether, petroleum ether, hexane, etc., is added to the concentrate, and the product thus precipitated is recovered by filtration. Further, the product is mixed with a solvent, such as 2-propanol, then stirred preferably for 30-60 minutes, the resulting product is collected by filtration and dried in vacuum to obtain a purified dicarboxylic acid diester.
Also when the dicarboxylic acid diester is synthesized from the dicarboxylic acid represented by R of the formula (3), the same procedures of reaction and purification of reaction liquids are followed as in using 2,2xe2x80x2-bis(trifluoromethyl)-4,4xe2x80x2-biphenyldicarboxylic acid mentioned above, whereby a purified dicarboxylic acid diester is obtained. The above-mentioned purification step is important for obtaining polyhydroxyamide resin of a high molecular weight.
In the present invention, the fluorine-containing polyhydroxyamide resin is produced by reacting one or two of the above-mentioned dicarboxylic acid diesters with one or two of the above-mentioned diamine components in an anhydrous organic solvent, such as tetrahydrofuran, N-methyl-2-pyrrolidone, xcex3-butyrolactone, etc., at preferably 60-90xc2x0 C. for preferably 3 hours or more, more preferably 24-36 hours. At this time, when a dicarboxylic acid diester obtained by using, in the group of compounds represented by the formulas (2), 4-nitrophenol or pentafluorophenol is employed, it is effective to carry out the reaction in the presence of an acid acceptive agent, such as triethylamine, N,N-dimethylaminobenzene, 4-dimethylaminopyridine, pyridine, etc.
The fluorine-containing polybenzoxazole resin of the present invention is produced by subjecting the fluorine-containing polyhydroxyamide resin obtained by the above-mentioned production process to heat-dehydrating ring closure.
The layer insulating film for multilayer interconnection according to the present invention can be produced by dissolving the fluorine-containing polyhydroxyamide resin obtained by the above-mentioned production process in an organic solvent to prepare a varnish of 5-40 wt % concentration, coating the varnish on a wafer or glass plate by such methods of coating as spin coating using a spinner, spray coating using a spray coater, dipping, printing, roll coating and the like to form a film, then drying the film preferably in an inert gas atmosphere at 300-500xc2x0 C. to obtain a fluorine-containing polyhydroxyamide resin film, and then subjecting the film to heat-dehydrating ring closure to obtain the intended fluorine-containing polybenzoxazole resin film. When a fluorine-containing polyhydroxyamide resin represented by the formula (1) is used, it is converted to a layer insulating film comprising fluorine-containing polybenzoxazole resin having the structure represented by the formula (6) by being subjected to heat-dehydrating ring closure.
The organic solvent which can be used for preparing the above-mentioned varnish may be commonly known aprotic polar organic solvents. Specific examples thereof include N,N-dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and xcex3-butyrolactone. The varnish may contain, according to necessity, various additives, for example, an adhesive agent, such as silane coupling agent, and a leveling agent typically represented by fluorine-containing compounds.
The present invention provides a layer insulating film for multilayer interconnection of semiconductors which comprises the fluorine-containing polybenzoxazole resin obtained by the above-mentioned production process.
The film comprising the fluorine-containing polybenzoxazole resin of a high molecular weight obtained according to the present invention has excellent performance characteristics in respect of heat resistance, mechanical strength and electric characteristics and is a film of great industrial value which can be used as the layer insulating film for multilayer interconnection of semiconductors.
The present invention is described in more detail below with reference to Examples, but the invention is in no way limited thereto.
The films prepared in Examples and Comparative Examples were used, to evaluate their characteristic properties, for determining the dielectric constant, heat resistance, coefficient of thermal expansion (CTE), water absorption and adhesion according to the following methods.
1. Dielectric Constant
Determination was made according to JIS K6911 at a frequency of 100 KHz by using HP-4284A. Precision LCR meter mfd. by Hewlett Packard Corp.
2. Heat Resistance
By using TG/DTA 220 mfd. by Seiko Instruments K.K. in an atmosphere of nitrogen gas stream of a flow rate of 200 ml/min and at a temperature increasing rate of 10xc2x0 C./min, the temperature at which the weight loss on heating reached 1% was determined.
3. Coefficient of Thermal Expansion
The coefficient of thermal expansion was determined in the temperature range of 25-100xc2x0 C. by using TMA/SS 120C mfd. by Seiko Instruments K.K. at a temperature increasing rate of 5xc2x0 C./min.
4. Water Absorption
According to JIS K6911, the ratio of weight change after immersion in pure water at 23xc2x0 C. for 24 hours was calculated.
5. Adhesion
According to JIS K5400 and using the crosscut tape method, the state of adhesion of each test piece was visually observed and evaluated in terms of xe2x80x9cthe number of peeled squares/the number of entire squaresxe2x80x9d